[Federal Register Volume 68, Number 152 (Thursday, August 7, 2003)]
[Notices]
[Pages 47104-47106]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-20151]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-443]
FPL Energy Seabrook, LLC, Seabrook Station, Unit 1; Exemption
1.0 Background
At the time that this exemption request was submitted (October
2002), North Atlantic Energy Service Corporation (NAESCO, or the
licensee) was the holder of Facility Operating License No. NPF-86 which
authorizes operation of the Seabrook Station, Unit No. 1 (Seabrook).
The license provides, among other things, that the facility is subject
to all rules, regulations, and orders of the U.S. Nuclear Regulatory
Commission (NRC, or the Commission) now, or hereafter, in effect.
On November 1, 2002, the Commission approved the transfer of the
license for Seabrook, to the extent held by NAESCO, and certain co-
owners of the facility, on whose behalf NAESCO was also acting, to FPL
Energy Seabrook, LLC (FPLE Seabrook). By letter dated December 20,
2002, FPLE Seabrook requested that the NRC continue to review and act
upon all requests before the Commission that had been submitted by
NAESCO.
The facility consists of a pressurized water reactor located in
Seabrook, New Hampshire.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR), part 50,
section 50.60(a), requires, in part, that except where an exemption is
granted by the Commission, all light-water nuclear power reactors must
meet the fracture toughness requirements for the reactor coolant
pressure boundary set forth in appendices G and H to 10 CFR part 50.
Appendix G to 10 CFR part 50 requires that pressure-temperature (P-T)
limits be established for reactor pressure vessels (RPVs) during normal
operating and hydrostatic or leak rate testing conditions.
Specifically, appendix G to 10 CFR part 50 states that ``The
appropriate requirements on both the pressure-temperature limits and
minimum permissible temperature must
[[Page 47105]]
be met for all conditions.'' Further, appendix G of 10 CFR part 50
specifies that the requirements for these limits are based on the
application of evaluation procedures given in Appendix G to Section XI
of the American Society of Mechanical Engineers (ASME) Boiler and
Pressure Vessel Code (Code). The provisions of ASME Code Case N-641
were incorporated in Appendix G of Section XI of the ASME Code in the
1998 Edition through the 2000 Addenda, which is the edition and addenda
of record in the 2003 Edition of 10 CFR part 50. However, in this case,
the licensee is still required to request an exemption to apply Code
Case N-641 since the Seabrook licensing basis has only been updated to
include the 1995 Edition through the 1996 Addenda of the ASME Code.
In order to address provisions of amendments to the Seabrook,
Technical Specification (TS) P-T limit curves, FPLE Seabrook requested,
in its submittal dated October 11, 2002, that the staff exempt Seabrook
from application of specific requirements of appendix G to 10 CFR part
50, and substitute use of ASME Code Case N-641. ASME Code Case N-641
permits the use of an alternate reference fracture toughness curve
(i.e., use of ``KIC fracture toughness curve'' instead of
``KIA fracture toughness curve,'' where KIC and
KIA are ``Reference Stress Intensity Factors,'' as defined
in ASME Code, Section XI, Appendices A and G, respectively) for RPV
materials and permits the postulation of a circumferentially-oriented
flaw for the evaluation of circumferential RPV welds when determining
the P-T limits. The proposed exemption request is consistent with, and
is needed to support, the Seabrook TS amendment that was contained in
the same submittal. The proposed Seabrook TS amendment will revise the
P-T limits for heatup, cooldown, and inservice test limitations for the
reactor coolant system (RCS) through 20 effective full-power years of
operation.
Code Case N-641
The licensee has proposed an exemption to allow use of ASME Code
Case N-641 in conjunction with Appendix G to ASME Section XI, 10 CFR
50.60(a) and 10 CFR part 50, appendix G, to establish the P-T limits
for the Seabrook RPV.
The proposed TS amendment to revise the P-T limits for Seabrook
relies, in part, on the requested exemption. These revised P-T limits
have been developed using the lower-bound KIc fracture
toughness curve shown in ASME Section XI, Appendix A, Figure A-2200-1,
in lieu of the lower-bound KIa fracture toughness curve of
ASME Section XI, Appendix G, Figure G-2210-1, as the basis fracture
toughness curve for defining the Seabrook P-T limits. In addition, the
revised P-T limits have been developed based on the use of a postulated
circumferentially-oriented flaw for the evaluation of RPV
circumferential welds, in lieu of the axially-oriented flaw which would
be required by Appendix G to Section XI of the ASME Code. The other
margins involved with the ASME Section XI, Appendix G process of
determining P-T limit curves remain unchanged.
Use of the KIc curve as the basis fracture toughness
curve for the development of P-T operating limits is more technically
correct than use of the KIa curve. The KIc curve
appropriately implements the use of a relationship based on static
initiation fracture toughness behavior to evaluate the controlled
heatup and cooldown process of a RPV, whereas the KIa
fracture toughness curve codified into Appendix G to Section XI of the
ASME Code was developed from more conservative crack arrest and dynamic
fracture toughness test data. The application of the KIa
fracture toughness curve was initially codified in Appendix G to
Section XI of the ASME Code in 1974 to provide a conservative
representation of RPV material fracture toughness. This initial
conservatism was necessary due to the limited knowledge of RPV material
behavior in 1974. However, additional knowledge has been gained about
RPV materials which demonstrates that the lower bound on fracture
toughness provided by the KIa fracture toughness curve is
well beyond the margin of safety required to protect the public health
and safety from potential RPV failure.
Likewise, the use of a postulated circumferentially-oriented flaw
in lieu of an axially-oriented one for the evaluation of a
circumferential RPV weld is more technically correct. The size of a
flaw required to be postulated for P-T limit determination has a depth
of one-quarter of the RPV wall thickness and a length six-times the
depth. Based on the direction of welding during the fabrication
process, the only technically-reasonable orientation for such a large
flaw is for the plane of the flaw to be circumferentially-oriented
(i.e., parallel to the direction of welding). Prior to the development
of ASME Code Case N-641 (and the similar ASME Code Case N-588), the
required postulation of an axially-oriented flaw for the evaluation of
a circumferential RPV weld has provided an additional and unnecessary
level of conservatism to the overall evaluation.
In addition, P-T limit curves based on the KIc fracture
toughness curve and postulation of a circumferentially-oriented flaw
for the evaluation of RPV circumferential welds will enhance overall
plant safety by opening the P-T operating window with the greatest
safety benefit in the region of low temperature operations. The
operating window through which the operator heats up and cools down the
RCS is determined by the difference between the maximum allowable
pressure defined by Appendix G of ASME Section XI, and the minimum
required pressure for the reactor coolant pump seals adjusted for
instrument uncertainties. A narrow operating window could potentially
have an adverse safety impact by increasing the possibility of
inadvertent overpressure protection system actuation due to pressure
surges associated with normal plant evolutions such as RCS pump starts
and swapping operating charging pumps with the RCS in a water-solid
condition.
Since application of ASME Code Case N-641 provides appropriate
procedures to establish maximum postulated defects and to evaluate
those defects in the context of establishing RPV P-T limits, this
application of the Code Case maintains an adequate margin of safety for
protecting RPV materials from brittle failure. Therefore, the licensee
concluded that these considerations were special circumstances pursuant
to 10 CFR 50.12(a)(2)(ii), which states: ``Application of the
regulation in the particular circumstances would not serve the
underlying purpose of the rule or is not necessary to achieve the
underlying purpose of the rule.''
In summary, the ASME Section XI, Appendix G procedure was
conservatively developed based on the level of knowledge existing in
1974 concerning reactor coolant pressure boundary materials and the
estimated effects of operation. Since 1974, the level of knowledge
about the fracture mechanics behavior of RCS materials has been greatly
expanded, especially regarding the effects of radiation embrittlement
and the understanding of fracture toughness properties under static and
dynamic loading conditions. The NRC staff concurs that this increased
knowledge permits relaxation of the ASME Section XI, Appendix G
requirements by application of ASME Code Case N-641, while maintaining,
pursuant to 10 CFR 50.12(a)(2)(ii), the underlying purpose of the ASME
Code and the NRC regulations to ensure an
[[Page 47106]]
acceptable margin of safety against brittle failure of the RPV.
The NRC staff has reviewed the exemption request submitted by FPLE
Seabrook and has concluded that an exemption should be granted to
permit the licensee to utilize the provisions of ASME Code Case N-641
for the purpose of developing Seabrook RPV P-T limit curves.
3.0 Discussion
Pursuant to 10 CFR 50.12, the Commission may, upon application by
any interested person or upon its own initiative, grant exemptions from
the requirements of 10 CFR part 50 when: (1) The exemptions are
authorized by law, will not present an undue risk to public health or
safety, and are consistent with the common defense and security; and
(2) when special circumstances are present.
Special circumstances, pursuant to 10 CFR 50.12(a)(2)(ii), are
present in that continued operation of Seabrook with the P-T limit
curves developed in accordance with ASME Section XI, Appendix G without
the relief provided by ASME Code Case N-641 is not necessary to achieve
the underlying purpose of appendix G to 10 CFR part 50. Application of
ASME Code Case N-641 in lieu of the requirements of ASME Code Section
XI, Appendix G provides an acceptable alternative methodology which
will continue to meet the underlying purpose of appendix G to 10 CFR
part 50. The underlying purpose of the regulations in appendix G to 10
CFR part 50 is to provide an acceptable margin of safety against
brittle failure of the RCS during any condition of normal operation to
which the pressure boundary may be subjected over its service lifetime.
The staff examined the licensee's rationale to support the
exemption request, and concluded that the use of ASME Code Case N-641
would satisfy 10 CFR part 50, section 50.12(a)(1) as follows:
(1) The requested exemption is authorized by law:
No law exists which precludes the activities covered by this
exemption request. The regulation 10 CFR part 50, section 50.60(b),
allows the use of alternatives to 10 CFR part 50, appendices G and H,
when an exemption is granted by the Commission pursuant to 10 CFR part
50, section 50.12.
(2) The requested exemption does not present an undue risk to the
public health and safety:
ASME Code Case N-641 permits the use of alternate reference
fracture toughness (KIC fracture toughness curve instead of
KIA fracture toughness curve) for RPV Materials in
determining the P-T limits. The use of the KIC curve
provides greater allowable fracture toughness than the corresponding
KIA curve. The other margins involved with the ASME Code,
Section XI, Appendix G process of determining P-T limit curves remain
unchanged.
Use of the KIC curve in determining the lower-bound
fracture toughness, which is, in turn, used in the development of the
P-T operating limits curve, models the slow heatup and cooldown process
of a reactor vessel. The KIC curve appropriately implements
the use of static initiation fracture toughness behavior to evaluate
the controlled heatup and cooldown process of an RPV.
Use of this approach is justified by the initial conservatism of
the KIA curve when it was codified in 1974. This initial
conservatism was necessary due to limited knowledge of RPV material
fracture toughness. Since 1974, additional knowledge has been gained
about the fracture toughness of vessel materials and their fracture
response to applied loads. The additional knowledge demonstrates that
the lower-bound fracture toughness provided by the KIA curve
is well beyond the margin of safety required to protect against
potential RPV failure. The lower-bound KIC fracture
toughness provides an adequate margin of safety to protect against
potential RPV failure and does not present an undue risk to public
health and safety.
(3) The requested exemption will not endanger the common defense
and security:
The common defense and security are not affected and, therefore,
not endangered by this exemption.
Based upon a consideration of the conservatism that is explicitly
incorporated into the methodologies of appendix G to 10 CFR part 50;
Appendix G to Section XI of the ASME Code; and Regulatory Guide 1.99,
Revision 2; the staff concluded that application of ASME Code Case N-
641, as described, would provide an adequate margin of safety against
brittle failure of the RPV. Therefore, the staff concludes that
pursuant to 10 CFR 50.12(a)(1), an exemption from the requirements of
10 CFR part 50, appendix G is appropriate, and that the methodology of
Code Case N-641 may be used to revise the P-T limits for the Seabrook
RPV.
4.0 Conclusion
Accordingly, the Commission has determined that, pursuant to 10 CFR
50.12(a), the exemption is authorized by law, will not present an undue
risk to the public health and safety, and is consistent with the common
defense and security. Also, special circumstances are present.
Therefore, the Commission hereby grants FPL Energy Seabrook, LLC an
exemption from the requirements of 10 CFR 50.60(a) and 10 CFR part 50,
Appendix G, to allow application of ASME Code Case N-641 in
establishing TS requirements for the reactor vessel pressure limits at
low temperatures for Seabrook.
Pursuant to 10 CFR 51.32, the Commission has determined that the
granting of this exemption will not have a significant effect on the
quality of the human environment (68 FR 44109).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 1st day of August, 2003.
For The Nuclear Regulatory Commission.
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear
Reactor Regulation.
[FR Doc. 03-20151 Filed 8-6-03; 8:45 am]
BILLING CODE 7590-01-P